The low fuel cost of a car has been conventionally carried out by reducing the rolling resistance of a tire (the improvement of rolling resistance). Request for the low fuel cost of a car has been recently strengthened and excellent low heat build-up property is requested for a rubber composition for producing tread, the ratio of tread occupied in a tire among tire members is high.
As methods of reducing the rolling resistance of tire tread, there are exemplified a method of compounding the specific amounts of 2 kinds of silica having different nitrogen adsorption specific surface areas (for example, Japanese Unexamined Patent Publication No.
2006-233177) and a method of compounding a modified styrene-butadiene rubber as a rubber component (for example, Japanese Unexamined Patent Publication No. 2006-56979).
Further, it is also known that heat build-up property is suppressed by increasing the compounding amount of sulfur. However, since strength at break TB and elongation at break EB of a rubber is lowered when the compounding amount of sulfur is increased, therefore there have been problems that tread crack is generated and the life time of tire tread is shortened when an obtained rubber composition is used for tire tread.
In other words, strength at break and low heat build-up property is contradictory physical property and it was difficult to satisfy both physical properties.